This invention relates to communications networks, particularly local area networks connecting office data processing equipment. In particular, it relates to a junction block for providing a splice-in connection such as a T-connection to a communication line requiring the use of shielded line because of the frequencies employed. Communication lines of the type concerned may comprise shielded twisted pair, coaxial cable, or shielded wire containing more than two conductors, among other types.
In the rapidly growing field of office automation, using electronic data processing equipment, there is a growing use of local area networks, serving, for example, a single office building or portion of a building. In such networks, there is increasing use of twisted-pair wire as the communications line. Frequently, when the network is installed in the building, such wire is strung through the building, for example, above the ceiling, and lines are dropped from the continuous line to floor level for the connection of equipment into the line. The drop line is typically terminated in a receptacle for a plug from the equipment to be connected into the line.
Prior art devices for such connection have had various disadvantages. Most significantly, such devices have been extremely expensive. For example, a method for connection that has been commonly used has involved terminating each arm of the T connection in a twin axial plug, each plug being then connected to the receptacle of a specially designed block. In addition to the cost of fabrication, such connections are obviously time-consuming to make, and require a high level of expertise. When the connector is employed in multiples in the course of wiring an entire building, the expense of manufacture and installation becomes significant.
It is therefore an object of this invention to provide a junction block for use with shielded two-conductor line or the like that is less expensive than prior art devices, both in production cost and in installation cost. It is a further object to provide such a junction block that can be installed without removal of the insulation of the inner conductors, or the individual preparation of such conductors, and that can be installed without special preparation of the shield, such as combing and pigtailing. Further, it is an object to provide such a junction block that can be used either in an intermediate or an end position on the line (as either a T-connection or an L-connection) or simply as a splice. It is a further object to provide such a block that is resistant to degrading the connection by exterior twisting forces on the network line. Finally, it is particularly an object to provide such a block which meets FCC requirements of limitations on noise generated from the block.
According to the invention, a junction block provides splice-in connection to a network line comprising an outer insulation, a shield, and at least two conductors, each conductor being separately enclosed in an insulation layer. The junction block comprises a base and cover mutually engageable to define a junction block body in an assembled condition. The block in its assembled condition provides at least two line-entrance structures connecting the interior and exterior of the block body. The base has an interior floor and perimeter wall portions; the base floor provides first bus receiving means and conductor bus receiving means. The block further comprises an electrically conductive shield bus positioned in the first bus receiving means, and providing a plurality of major slots, each major slot being aligned with a line-entrance structure. Each major slot is sized to displace the outer insulation and engage the shield of a network line.
The block further comprises electrically conductive conductor buses each positioned in the conductor bus receiving means and having an upper edge spaced from the receiving means, and providing at least one slot opening from the upper edge, each slot being sized to displace the inner insulation and engage the conductor of a network line.
The cover has an inner surface, providing conductor keepers, generally aligned with the conductor buses in the assembled condition of the block, each conductor keeper extending towards the base floor by a distance less than the depth of the conductor bus slots.
In preferred embodiments, the junction block has three line-entrance structures, two of them being generally aligned. The shield bus is generally U-shaped, comprising two leg portions each adjacent one of the generally aligned line-entrance structures, and an included portion adjacent the remaining line-entrance structure; the portions are of generally equal length, each providing one of the shield bus major slots. The shield bus major slots extend vertically away from the base floor; the conductor bus slots also extend vertically away from the base floor. The base provides three network line receiving slots, and the block cover provides three corresponding line retaining legs; a retaining leg is received in a receiving slot in the block assembled condition to comprise a line entrance structure. The retaining legs together with the line receiving slots together define a polarized assembled position of the cover with respect to the base.
The line receiving slots each provide a plurality of ridges oriented parallel with the extent of the line-entrance structure, and the retaining legs provide a plurality of ridges similarly oriented; the slot ridges and leg ridges together comprise line rotation-limiting structure.
The U-shaped shield bus defines an area parallel with the plane of the base floor, effectively enclosed within the shield bus, the two inner conductor buses being positioned in the base conductor bus receiving means to define a point of closest approach between the conductor buses; the point of closest approach is within the effectively enclosed area.
Preferably, in the assembled condition of the block, the junction block body has an axis of symmetry in a plane parallel with the base floor, and the two aligned line-entrance structures are positioned symmetrically with respect to the axis of symmetry; the bus shield portions are positioned symmetrically with respect to the axis of symmetry, and the conductor buses are positioned symmetrically with respect to the axis of symmetry.